Power saving system for rotating disk data storage apparatus

ABSTRACT

A flexible magnetic disk drive is disclosed which has a stepper motor coupled to a data transducer via a steel belt motion translating mechanism for moving the transducer from track to track on the rotating disk in response to stepping pulses and a stepping direction signal from an external host system. In order to save power, the stepper motor is held deenergized while the disk drive motor is out of rotation, with the consequent possibility that the transducer may be displaced from the required track position on the disk while the stepper motor is held deenergized. Therefore, in order to always memorize the latest of the successive destination tracks commanded by the host system, a forward/backward counter is provided which counts the external stepping pulses in either direction depending upon the binary state of the external stepping direction signal. After the disk drive motor is set into rotation, stepping pulses and an stepping direction signal are generated internally for causing the stepper motor to automatically reposition the transducer on the memorized latest destination track.

BACKGROUND OF THE INVENTION

Our invention relates generally to an apparatus having a data transduceror transducers driven by an electric seek motor for accessing any of amultiplicity of concentric annular record tracks on a rotating disklikerecord medium such as a flexible magnetic disk which may be packaged incassette or cartridge form. More specifically, our invention deals witha method of, and means for, saving power in such a rotating disk datastorage apparatus by holding the seek motor unenergized when the datatransducer or transducers are not in track seek operation.

Generally, in rotating disk data storage apparatus of the type underconsideration, the seek motor takes the form of either a voice coilmotor or a stepper motor. Our invention particularly concerns apparatusof the class employing the stepper motor for causing the data transduceror transducers to move to any desired tracks on the disk or disks.

The stepper motor has a rotor that rotates in short and essentiallyuniform angular movements, rather than continuously, in response tostepping pulses supplied from a host system external to the data storageapparatus. The stepwise rotation of the stepper motor is converted by amotion translating mechanism into the linear stepwise travel of thetransducer or transducers for track to track accessing on the disk ordisks. There are, here again, two familiar examples of the motiontranslating mechanism: one employs a lead screw, and the other a steelbelt. An example of steel belt type motion translating mechanism isdescribed and claimed in U.S. Pat. No. 4,774,611 filed by Ando andassigned to the assignee of the instant application.

The stepper motor need not be held energized throughout each period ofoperation of the data storage apparatus as the motor is used only formoving the transducer or transducers from track to track on the disk ordisks. The continued energization of the stepper motor would involve asubstantial waste of energy. It has therefore been suggested to hold thestepper motor unenergized when the transducer or transducers are out ofseek operation. U.S. Pat. No. 4,783,706 filed by Shoji et al. andassigned to the assignee of our present application describes and claimssuch a power saving method and electronics for implementing the method.

We have found that the noted Shoji et al. U.S. patent has a drawbackwhen the stepper motor is used in combination with the steel belt motiontranslating mechanism. The drawback arises because of the smaller detenttorque exerted by the steel belt on the stepper motor than by the leadscrew when the motor is disconnected from the power supply.Consequently, in event mechanical vibrations or shocks are applied tothe stepper motor when it is unenergized, the rotor of the stepper hasbeen very liable to be displaced with respect to the fixed motorwindings, being no longer electromagnetically retained in the requiredangular position. Thus the transducer or transducers coupled to therotor via the steel belt motion translating mechanism have been easy tobe displaced from the required track positions on the disk or disks.

SUMMARY OF THE INVENTION

We have hereby invented how to avoid the waste of energy due to thecontinuous energization of the seek motor in rotating disk data storageapparatus of the type in question without giving rise to the notedproblem heretofore encountered when the seek motor is coupled to thedata transducer or transducers via a motion translating mechanism thatexerts a relatively small detent torque on the motor.

Briefly stated in one aspect thereof, our invention concerns a powersaving method for a data storage apparatus having a data transducer fordata transfer with a disklike record medium having a multiplicity ofannular data storage tracks arranged concentrically on at least one sidethereof, the apparatus further having a disk drive motor for setting therecord medium into rotation when a binary "motor on" signal is in afirst state, and out of rotation when the "motor on" signal is in asecond state, and a seek motor for causing the transducer to travel fromtrack to track on the record medium. The power saving method of ourinvention dictates the deenergization of the seek motor when the "motoron" signal is in the second state, that is, when the disk drive motor isout of rotation. Since the transducer may be displaced from the requiredtrack position on the record medium while the seek motor is helddeenergized, the latest of successive destination tracks represented byseek data, which are normally supplied when the "motor on" signal is inthe first state, is always memorized. Each time the "motor on" signalregains the first state, the transducer is automatically repositioned onthe memorized latest destination track on the record medium.

Usually, when a stepper motor is employed as the seek motor, the seekdata are supplied by an external host system in the form of steppingpulses and a stepping direction signal. A stepper motor control circuitresponds to the external stepping pulses and the external steppingdirection signal by correspondingly controlling the stepper motor via astepper motor drive circuit. Therefore, for repositioning the transduceron the latest destination track, we suggest that the apparatus beconstructed to internally generate stepping pulses and a steppingdirection signal which are similar respectively to the external steppingpulses and the external stepping direction signal. The internal steppingpulses and stepping direction signal may then be applied to the steppermotor control circuit after the "motor on" signal regains the firststate, thereby causing the stepper motor to reposition the transducer.This scheme is preferred because not only the stepper motor but also itscontrol circuit and drive circuit can all be used both for track seekoperation in response to the external stepping signals and for therepositioning of the transducer in response to the internal steppingsignals according to our invention.

At the time the "motor on" signal regains the first state, the currentposition of the transducer on the disk is first unknown because it mayhave been displaced from the latest destination track while the "motoron" signal has been in the second state. The transducer may therefore betemporarily moved to an endmost reference track on the disk and thenceto the memorized latest destination track.

It is also possible according to the power saving method of ourinvention to incorporate two power supplies, having different supplyvoltages, in the stepper motor drive circuit. The stepper motor may beenergized from the higher power supply for track seeking, and from thelower power supply for holding the transducer in position on the diskwhen the "motor on" signal is in the first state but when no externalstepping pulses are being supplied. The stepper motor may bedisconnected from both power supplies when the "motor on" signal gainsthe second state. After the "motor on" signal subsequently regains thefirst state, the transducer can be repositioned on the memorized latestdestination track, with the stepper motor energized from the higherpower supply while being driven by the internal stepping signals.

Another aspect of our invention concerns a rotating disk data storageapparatus constructed for carrying out the power saving methodsummarized above. Characteristically, the apparatus comprises a powerswitching circuit for causing the seek motor to be energized from apower supply when the "motor on" signal is in the first state, and to bedeenergized when the "motor on" signal is in the second state, memorymeans for storing the latest of the successive destination tracksrepresented by the external seek data, and repositioning circuit meansfor automatically repositioning the transducer on the memorized latestdestination track after the "motor on" signal regains the first state.

We recommend the use of a simple forward/backward counter as the memorymeans in the case where a stepper motor is employed as the seek motor.Since external stepping pulses and an external stepping direction signalare supplied as aforesaid from the external host system to the steppermotor control circuit for driving the stepper motor during trackseeking, the forward/backward counter may count the external steppingpulses in either an increasing or a decreasing direction depending uponthe binary state of the external stepping direction signal which isindicative of whether the transducer is to be moved radially inwardly oroutwardly of the data storage disk. It is possible in this manner forthe forward/backward counter to store always the latest of thesuccessive destination tracks represented by the external steppingpulses and stepping direction signal.

The repositioning circuit means may comprise generators for generatinginternal stepping pulses and an internal stepping direction signal whichare similar respectively to the external stepping pulses and theexternal stepping direction signal. The internal stepping pulses andstepping direction signal may both be applied to the stepper motorcontrol circuit for repositioning the transducer on the memorized latestdestination track after the "motor on" signal regains the first state.

We suggest the use of a second forward/backward counter for suchrepositioning of the transducer. As has been mentioned in connectionwith the foregoing summary of the method of our invention, thetransducer is to be first moved to an endmost reference track on thedisk before being repositioned on the latest destination track.Therefore, reset when the transducer arrives at the endmost referencetrack, the second forward/backward counter may start counting theinternal stepping pulses in either an increasing or a decreasingdirection depending upon the binary state of the internal steppingdirection signal. Thus the counter will provide an output representativeof the current position of the transducer on the disk. Outputs from bothfirst and second forward/backward counters may be constantly compared,and the delivery of the internal stepping pulses to the stepper motorcontrol circuit may be discontinued when the two outputs agree, that is,when the transducer is repositioned on the latest destination track.

We have thus succeeded in repositioning the transducer by making utmostuse of the existing parts of the data storage apparatus. Moreover, aswill become apparent from the subsequent description of preferredembodiments, the data storage apparatus incorporating the repositioningmeans is fully compatible with host systems of standard design.

The above and other features and advantages of our invention and themanner of realizing them will become more apparent, and the inventionitself will best be understood, from a study of the followingdescription and appended claims, with reference had to the attacheddrawings showing the preferred embodiments of our invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the rotating disk data storage apparatusconstructed in accordance with the novel concepts of our invention;

FIG. 2 is a schematic electrical diagram showing in more detail astepper motor, a stepper motor drive circuit, and a power switchingcircuit, all included in the FIG. 1 apparatus;

FIG. 3 is a block diagram showing in more detail the repositioningcircuit of the FIG. 1 apparatus;

FIG. 4, consisting of (A)-(H), is a combined waveform and timing diagramexplanatory of the operation of the FIG. 1 apparatus;

FIG. 5 is a partial schematic electrical diagram of another preferredform of rotating disk data storage apparatus according to our invention;and

FIG. 6, consisting of (A)-(D), is a combined waveform and timing diagramexplanatory of the operation of the FIG. 5 apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We will now describe our invention in detail as embodied in the datastorage apparatus for use with a flexible magnetic disk of five and aquarter inch diameter. The representative data storage apparatus, ordisk drive according to common parlance, is generally designated 10 inFIG. 1 and therein shown together with the flexible magnetic disk 12replaceably held in position therein by a drive hub assembly 14. A diskdrive motor 16 is shown coupled directly to the drive hub assembly 14for imparting rotation to the disk 12. A motor control and drive circuit20 is connected to the disk drive motor 16 for controllably energizingthe same. An index sensor 22 is provided for sensing an index mark onthe disk 12 for providing a signal indicative of the angular positionand velocity of the disk. The index mark is shown as a hole 24 formedeccentrically in the disk 12, and the index sensor 22 as an opticalsensor of well known design comprising a light source 26 and aphotoreceptor 28.

We assume for the convenience of disclosure that the disk 12 is singlesided, having a multiplicity of concentric annular record tracks formedon one side only. Thus the apparatus 10 has but one data transducer 30disposed opposite the track bearing surface of the disk 12. For movingthe transducer 30 across the record tracks on the disk 12, a seek motor32 is coupled to the transducer via a motion translating mechanism 34.

We also assume that in this embodiment of our invention, the seek motor32 takes the form of a bidirectional, four phase stepper motor, and themotion translating mechanism 34 the steel belt device described andclaimed in Ando U.S. Pat. No. 4,774,611, supra. The incremental rotationof the stepper motor 32 is translated by the steel belt motiontranslating mechanism into the linear stepwise travel of the transducer30 from track to track on the disk 12. At 36 is seen a conventional"track zero" sensor capable of optically detecting the fact that thetransducer 30 is over the outmost Track Zero on the disk 12 orthereabout.

The stepper motor 32 is driven by a motor drive circuit 38 under thecontrol of a motor control circuit 40. A power switching circuit 42 isalso connected to the stepper motor drive circuit 38 for the on/offpower control of the stepper motor 32 according to our invention.

We have shown the disk drive 10 together with a host system 44 ofstandard design which controls its operation. The host system 44 isconnected to the disk drive 10 via three output lines 46, 48 and 50 andtwo input lines 52 and 54. The output line 46 is for the delivery of a"motor on" signal indicative of whether the disk drive motor 16 is to beset into or out of rotation. The output line 48 is for the delivery ofstepping pulses for causing the incremental rotation of the steppermotor 32. The output line 50 is for the delivery of a stepping directionsignal indicative of the direction of rotation of the stepper motor 32.The input line 52 is for inputting a "ready" signal indicative ofwhether the disk 12 is ready for the commencement of data transfer withthe transducer 30. The input line 54 is for inputting read data.Actually, there are many more signal lines between disk drive 10 andhost system 44. We have not shown such additional signal lines becausethey have no direct pertinence to our invention.

As is standard in the disk drive art, the number of stepping pulses overthe line 48 represents the number of record tracks on the disk 12 to betraversed by the transducer 30. The stepping direction signal over theline 50 is a binary signal, having a binary zero state for causing thetransducer 30 to travel radially outwardly of the disk 12, and a binaryone state for causing the transducer to travel radially inwardly of thedisk. Thus the stepping pulses and the stepping direction signalconstitute in combination seek data representative of a destinationtrack on which the transducer 30 is to be positioned by the steppermotor 32 in cooperation with the steel belt motion translating mechanism34.

The stepping pulse line 48 and the stepping direction signal line 50 areboth connected to a track counter 56 via respective NOT circuits 58 and60. The track counter 56 is a forward/backward counter, also known as abidirectional counter, capable of counting input pulses in either anincreasing or a decreasing direction. More specifically, the trackcounter 56 counts the stepping pulses in an increasing direction whenthe stepping direction signal is in a binary one state, commanding thetransducer 30 to travel radially inwardly of the disk 12, and in adecreasing direction when the stepping direction signal is in a binaryzero state commanding the transducer to travel radially outwardly of thedisk. Thus the track counter 56 serves as a memory for storing thesuccessive destination tracks commanded by the host system 44.Constantly updated, the track counter 56 will memorize only the latesttrack command from the host system 44.

Besides being connected to the track counter 56 as above, the steppingpulse line 48 and the stepping direction signal line 50 must beconnected to the stepper motor control circuit 40 in order to enable thelatter to generate the stepper motor control signals in response to thestepping pulses and the stepping direction signal. However, in this diskdrive 10, the control circuit 40 must input not only the stepping pulsesand the stepping direction signal from the external host system 44 butalso those generated internally, within the disk drive itself, forrepositioning the transducer 30 on the disk 12 according to ourinvention, as will be detailed subsequently.

Accordingly, the outputs of the NOT circuits 58 and 60 are connected tothe stepper motor control circuit 40 via a stepping signal selectorcircuit 62 which permits selective passage therethrough of the externalstepping pulses and stepping direction signal and the internal steppingpulses and stepping direction signal. The stepping signal selectorcircuit 62 has a first output line 64 for delivery of the external orinternal stepping pulses to the stepper motor control circuit 40, and asecond output line 66 for delivery of the external or internal steppingdirection signal to the stepper motor control circuit. The stepper motorcontrol circuit 40 conventionally responds to the incoming steppingpulses and stepping direction signal for supplying four phase controlsignals to the stepper motor drive circuit 38 thereby causing the sameto drive the stepper motor 32 accordingly.

The power switching circuit 42 functions as aforesaid for the on/offcontrol of power fed from drive circuit 38 to stepper motor 32. In orderto perform this function the power switching circuit 42 has an inputconnected to the stepping pulse output line 64 of the stepping signalselector circuit 62, and another input connected to the "motor on"signal output line 46 of the host system 44 via a NOT circuit 68.

We have diagramed in more detail in FIG. 2 the stepper motor 32, thestepper motor drive circuit 38 and the power switching circuit 42 aswell as their interconnections. Although the diagram is highlyschematic, it will nevertheless be seen that the stepper motor 32 hasfour phase fixed windings 70 to be excited one at a time to causeincremental rotation of a rotor, not shown, which is coupled to the datatransducer 30 via the steel belt motion translating mechanism 34.

It will be also noted from FIG. 2 that the stepper motor drive circuit38 has two power supplies, a low power supply 72 and a high power supply74, in this particular embodiment. Typically, the low power supply 72provides a supply voltage of five volts, and the high power supply 74that of twelve volts. The power switching circuit 42 connects the highpower supply 74 to the stepper motor 32 for energizing its windings 70during track seek operation, and the low power supply 72 to the steppermotor for energizing its windings in order to electromagnetically holdthe transducer 30 on the required track on the disk 12 during therotation of the disk drive motor 14, as will become better understood asthe description progresses.

The four phase windings 70 of the stepper motor 32 are interconnected,each at one extremity thereof, for joint connection to the powerswitching circuit 42 and thence to either of the low power supply 72 andhigh power supply 74. The other extremities of the stepper motorwindings 70 are grounded via respective switching transistors 76included in the stepper motor drive circuit 38. The bases of all thetransistors 76 are separately connected to the stepper motor controlcircuit 40 for receiving therefrom the motor control signals that havebeen formed in response to the external or internal stepping pulses fromthe signal selector circuit 62. Thus, upon conduction of the fourswitching transistors 72 in response to the motor control signals, thefour phase windings 70 of the stepper motor 32 are to be excited byeither of the two power supplies 72 and 74, provided that the motorwindings are electrically connected to either of the power supplies bythe power switching circuit 42. The sequential excitation of the motorwindings 70 results in the incremental rotation of the unshown rotor.

The power switching circuit 42 includes two electronically actuablepower switches 78 and 80, such as transistors, connected respectivelybetween the low power supply 72 and high power supply 74 of the steppermotor drive circuit 38 and the interconnected extremities of the steppermotor windings 70. Also included in the power switching circuit 42 aremeans for the on/off control of the power switches 78 and 80 in responseto the external or internal stepping pulses from the signal selectorcircuit 62 and to the inverted "motor on" signal from the NOT circuit 68on the "motor on" output line 46 of the host system 44. Such meansinclude a retriggerable monostable multivibrator (RMMV) 82, a NOTcircuit 84 and an AND gate 86.

The RMMV 82 has an input connected to the stepping pulse output line 64of the stepping signal selector circuit 62. The output of the RMMV isconnected directly to the high power switch 80 on one hand and, on theother hand, to the low power switch 78 via the NOT circuit 84 and theAND gate 86. The other input of the AND gate 86 is connected to the"motor on" output line 46 of the host system 44 via the NOT circuit 68.

The RMMV 82, per se well known in the art, is normally low, goes highwhen triggered by each external or internal stepping pulse, and remainshigh for a predetermined time before returning to the low state in whichit is stable. The predetermined time during which the RMMV remains inthe unstable high state is longer than the cycle of the stepping pulses.Accordingly, when triggered by a series of external or internal steppingpulses, the RMMV will go high in response to the first pulse and remainso until the lapse of the predetermined time following the last pulse ofthe series. The high power switch 80 will be held closed as long as theRMMV 82 remains high, connecting the high power supply 74 to the steppermotor windings 70. It is thus seen that the stepper motor 32 isenergized from the high power supply 74 for driving the transducer 30both in its track seek operation in response to the external steppingpulses from the host system 44, and in its transducer repositioningoperation in response to the internal stepping pulses.

Since the RMMV 82 is connected to the AND gate 86 via the NOT circuit84, the low power switch 78 is open when the RMMV is high in response tothe stepping pulses, that is, when the high power switch 80 is closed.The low power switch 78 is also open when the NOT circuit 68, FIG. 1, islow, that is, when the "motor on" signal is high, commanding the diskdrive motor 16 to be held out of rotation. In other words, the low powerswitch 78 is closed only when the "motor on" signal is low, commandingthe rotation of the disk drive motor 16, and when, at the same time, thepower switching circuit 42 is receiving no external or internal steppingpulses. The consequent energization of the stepper motor 32 from the lowpower supply 72 during such periods is effective to hold the transducer30 in position on the disk 12.

As will be apparent from the foregoing, the stepper motor 32 is helddeenergized from either of the power supplies 72 and 74 when the diskdrive motor 16 is out of rotation, unless then the host system 44delivers stepping pulses to the disk drive 10. With the stepper motor 32thus held completely deenergized for saving power, the unshown rotor ofthe stepper motor may be angularly displaced with respect to the motorwindings 70 because of the low detent torque exerted thereon by thesteel belt motion translating mechanism 34, resulting in thedisplacement of the data transducer 30 from the required track positionon the magnetic disk 12.

We have employed the track counter 56, FIG. 1, in order to overcome thisinconvenience. Since the track counter 56 memorizes the latestdestination track commanded by the host system 44, the data transducer30 can be automatically repositioned on this destination track on thedisk 12 even if it has been displaced in either direction therefromwhile the stepper motor 32 has been held unenergized, as will bediscussed in more detail hereafter. Incidentally, the host system 44 maydeliver stepping pulses while the "motor on" signal is high, commandingthe disk drive motor 16 to be held out of rotation. In this case thehigh power switch 80 will become closed thereby connecting the highpower supply 74 to the stepper motor windings 70.

For such automatic repositioning of the transducer 30 on the latestdestination track on the disk 12, we have employed, in addition to thetrack counter 56, a repositioning circuit 88, a second track counter 90,a digital comparator 92 and a "track zero" detector circuit 94, all asshown in FIG. 1.

As illustrated in more detail in FIG. 3, the repositioning circuit 88comprises an internal stepping pulse generator 96, an internal steppingdirection signal generator 98 and a repositioning state signal generator100. As the name implies, the repositioning state signal generator 100generates a signal indicative of whether the transducer 30 is beingrepositioned on the disk 12 after possible accidental displacement fromthe latest destination track while the stepper motor 32 has been heldcompletely deenergized. These generators 96, 98 and 100 are connected tothe outputs a, b and c, respectively, of the repositioning circuit 88.The generators 96-100 are also jointly connected to a reset input d forinputting the inverted "motor on" signal from the NOT circuit 68, FIG.1, so that the generators are all reset when the "motor on" signal goeslow, commanding the disk drive motor 16 to be set into rotation.

It will also be noted from FIG. 3 that the generators 96-100 are allconnected to a repositioning start signal input e and to a repositioningcomplete signal input f. These inputs e and f are for inputting signalsfor causing the generators 96-100 to start and end, respectively, theproduction of the noted signals for repositioning the transducer 30. Therepositioning start signal input e is connected to a motor currentdetector circuit, not shown, built into the disk drive motor control anddrive circuit 20. The repositioning complete signal input f is connectedto the (A=B) output of the comparator 92.

The internal stepping direction signal generator 98 is additionallyconnected to a step in input g, a step out input h and an additionalinput i. The step in input g and step out input h are connected to the(A<B) output and (A>B) output, respectively, of the comparator 92. Theadditional input i is connected to the "track zero" detector circuit 94.

The second track counter 90 is connected to the outputs a and b of therepositioning circuit 88 for inputting the internal stepping pulses andthe internal stepping direction signal therefrom. Like the first trackcounter 56, this second track counter 90 is also a forward/backwardcounter. Thus the second track counter 90 counts the internal steppingpulses in an increasing direction when the internal stepping directionsignal is high, commanding the transducer 30 to travel radially inwardlyof the disk 12, and in a decreasing direction when the internal steppingdirection signal is low, commanding the transducer to travel radiallyoutwardly of the disk. The second track counter 90 has a reset inputconnected to the "track zero" detector circuit 94.

It will be recalled that the first track counter 56 serves as a memoryfor storing the latest track position of the transducer 30 commanded bythe external host system 44. The second track counter 90, then, servesto register the current track position of the transducer 30 beingrepositioned on the disk 12 in response to the internal stepping pulsesand stepping direction signal from the repositioning circuit 88.

The digital comparator 92 has two inputs connected respectively to thefirst and the second track counters 56 and 90. Let A be the output fromthe first track counter 56, and B the output from the second trackcounter 90. It will be seen, then, that A represents the latestdestination track commanded by the host system 44, and B the currenttrack position of the transducer 34 being repositioned by the internalstepping pulses and stepping direction signal. The comparator 90produces a high output from its (A>B) output when A is greater than B,from its (A<B) output when A is less than B, and from its (A=B) outputwhen A is equal to B. Functionally, therefore, the comparator 90determines whether the transducer 30 is positioned radially inwardly oroutwardly of, or on, the destination track while being repositioned onthe disk 12.

The stepping signal selector circuit 62 comprises four AND gates 102,104, 106 and 108, two OR gates 110 and 112, and a NOT circuit 114. TheAND gate 102 has an input connected to the NOT circuit 58, and anotherinput to the output c of the repositioning state signal generatorcircuit 100, FIG. 3, of the repositioning circuit 88. The output of theAND gate 102 is connected to the OR gate 110 and thence to the steppingpulse input of the stepper motor control circuit 40. Therefore, theselector circuit 62 will permit the passage of the external steppingpulses from the host system 44 on to the stepper motor control circuit40 when the transducer 30 is not being repositioned.

The AND gate 104 has a first input connected to the internal steppingpulse output a of the repositioning circuit 88, and another inputconnected via the NOT circuit 114 to the repositioning state signaloutput c of the repositioning circuit 88. The output of the AND gate 104is connected to the OR gate 110 and thence to the stepping pulse inputof the stepper motor control circuit 40. Thus the selector circuit 62will permit the passage of the internal stepping pulses from therepositioning circuit 88 on to the stepper motor control circuit 40 onlywhen the transducer 30 is being repositioned.

The AND gate 106 has an input connected to the NOT circuit 60, andanother input connected to the repositioning state signal output c ofthe repositioning circuit 88. The output of the AND gate 106 isconnected to the OR gate 112 and thence to the stepping direction signalinput of the stepper motor control circuit 40. Accordingly, the selectorcircuit 62 will permit the passage of the external stepping directionsignal from the host system 44 on to the stepper motor control circuit40 when the transducer 30 is not being repositioned.

The AND gate 108 has an input connected to the stepping direction signaloutput b of the repositioning circuit 88, and another input connectedvia the NOT circuit 114 to the repositioning state signal output c ofthe repositioning circuit. The output of the AND gate 108 is connectedto the OR gate 112 and thence to the stepping direction signal input ofthe stepper motor control circuit 40. Thus the selector circuit 62 willpermit the passage of the internal stepping direction signal from therepositioning circuit 88 on to the stepper motor control circuit 40 whenthe transducer 30 is being repositioned.

We have stated that the "track zero" detector circuit 94 forms a part ofthe means for automatically repositioning the transducer 30 on thelatest destination track on the disk 12. The detection of the fact thatthe transducer 30 is on Track Zero on the disk is necessary because thetransducer must be temporarily returned to that track before beingrepositioned on the latest destination track, as will become apparentfrom the subsequent description of operation.

As will be noted from FIG. 1, the "track zero" detector circuit 94 hastwo inputs, one connected to the "track zero" sensor 36, and the otherto the first phase control output line of the stepper motor controlcircuit 40. This is because the optical "track zero" sensor 36 is byitself incapable of accurately sensing the fact that the transducer 30is on Track Zero on the disk 12, relying as it does on the position of alinearly movable member of the motion translating mechanism 34 towardthat end.

Therefore, with a view to the more accurate detection of the "trackzero" position of the transducer 30 on the disk 12, the optical "trackzero" sensor 36 is connected to the "track zero" detector circuit 94along with the first phase control output line of the stepper motorcontrol circuit 40. We presuppose in making the above statement that thestepper motor 32 has its first phase windings energized when thetransducer 30 is on Track Zero on the disk 12, according to standardpractice in the art. The "track zero" detector circuit 94 determinesthat the transducer 30 is on Track Zero when the "track zero" sensor 36indicates that the transducer is in that position and when, at the sametime, the stepper motor control circuit 40 puts out the first phasecontrol signal to the stepper motor drive circuit 38 to cause excitationof the first phase windings.

After the transducer 39 has been repositioned on the latest destinationtrack, too, the host system 44 must be informed of the fact that thedisk drive 10 has become ready for the commencement of data transferbetween disk 12 and transducer 30. We have employed to this end a"ready" counter 116 and a NAND gate 118. The "ready" counter 116 has aninput connected to the index sensor 22 for counting the index pulses,and a reset input connected to the NOT circuit 68 for inputting theinverted "motor on" signal. Therefore, after having been reset when the"motor on" signal goes high, the "ready" counter 116 goes high when apredetermined number (e.g. two) of index pulses are received, that is,when the disk 12 picks up speed to a predetermined degree.

The NAND gate 118 has an input connected to the "ready" counter 116,another input connected to the repositioning state signal output c ofthe repositioning circuit 88, and still another input connected via aNOT circuit 120 to the drive select output line 122 of the host system44. The output of the NAND gate 118 is connected to the "ready" inputline 52 of the host system 44.

The repositioning state signal goes high upon completion of therepositioning of the transducer 30. As is standard in the disk driveart, drive select signals are needed when two or more disk drives aredaisy chained to the host system 44, in order to enable the host systemto select whichever of the disk drives for data transfer with theassociated disk. Consequently, the NAND gate 118 will go low, informingthe host system 44 that the disk drive 10 is ready for the commencementof data transfer with the disk 12, when: (a) the "ready" counter 116goes high to indicate that the disk 12 has picked up speed to apredetermined degree; (b) the repositioning state signal output c of therepositioning circuit 88 goes high to indicate the completion oftransducer repositioning; and, at the same time, (c) the inverted driveselect signal from the NOT circuit 120 goes high to choose this diskdrive 10 for data transfer with the disk 12.

The disk drive 10 conventionally includes a read/write circuit 124connected to the transducer 30. The read/write circuit 124 comprises awrite circuit for supplying to the transducer 30 a write currentrepresentative of write data fed over a line 126, and a read circuit forprocessing the output from the transducer into well defined pulsesrepresentative of the read data. A drive circuit 128 for electricallypowering the read/write circuit 124 is connected via the NOT circuit 68to the "motor on" output line 46 of the host system 44. The drivecircuit 128 powers the read/write circuit 124 only when the "motor on"signal is low, commanding the rotation of the disk drive motor 16, sincethe read/write circuit needs to be so powered only during the progressof data transfer between disk 12 and transducer 30. Power consumption bythe read/write circuit 124 is thus reduced to a minimum required.

The read data output of the read/write circuit 124 is connected to thehost system 44 via a NAND gate 130. This NAND gate has another inputconnected via the NOT circuit 120 to the drive select output line 122 ofthe host system 44, yet another input connected to the repositioningstate signal output c of the repositioning circuit 88, and still anotherinput connected to the "ready" counter 116. Therefore, the read data issent into the host system 44 only when all the following conditions aremet: (a) the "ready" counter 116 is high to indicate that the disk 12has picked up speed to a predetermined degree; (b) the repositioningstate signal is high to indicate the completion of transducerpositioning; and (c) the inverted drive select signal is high to choosethis disk drive 10 for data transfer with the associated disk 12.

OPERATION

We will refer to the combined waveform and timing diagram of FIG. 4 forthe description of operation of the disk drive 10 constructed as shownin FIGS. 1-3. We have plotted this diagram on the assumption that thedisk drive motor 16 has been in rotation before a time t₁, with the"motor on" signal held low as at (A) in FIG. 4. The transducer 30 hasbeen positioned on some track Tn on the disk 12, as at (H) in FIG. 4,according to the latest destination track command from the host system44. This latest destination track Tn will have been memorized asaforesaid by the first track counter 56 on the basis of the externalstepping pulses and stepping direction signal that have been fed fromthe host system 44 via the NOT circuits 58 and 60.

Also, before the time t₁, the stepper motor 32 has been energized fromthe low power supply 72, FIG. 2, of the stepper motor drive circuit 38,as at (D) in FIG. 4. This is because the low power switch 78 is closedwhen the "motor on" signal is low (inverted "motor on" signal high) andwhen, at the same time, no external or internal stepping pulses arebeing generated. The energization of the stepper motor 32 from the lowpower supply 72 is effective to hold the transducer 30 on the latestdestination track Tn.

The "motor on" signal from the host system 44 is shown to go high at thetime t₁. Then, as the NOT circuit 68 on the "motor on" line 46 goes low,the control and drive circuit 20 will deenergize the disk drive motor 16as at (C) in FIG. 4.

Moreover, as will be understood by referring back to FIG. 2, the ANDgate 86 of the power switching circuit 42 will be disabled by the lowoutput from the NOT circuit 68. The power switch 78 will then open todisconnect the low power supply 72 from the stepper motor windings 70.The other power switch 80 is, of course, open since neither external norinternal stepping pulses are now being supplied from the stepping signalselector circuit 62. Thus, as indicated at (D) in FIG. 4, the steppermotor 32 will become completely deenergized at the time t₁ in order tosave power. The "motor on" signal is shown to remain high until a timet₂. The stepper motor 32 is to be held disconnected from both powersupplies 72 and 74 during this time interval t₁ -t₂, provided that nostepping pulses are received from the host system 44.

Rarely will the host system 44 put out stepping pulses while the "motoron" signal is high, as during the period t₁ -t₂ in FIG. 4. Let us,however, assume a rare case where three stepping pulses are receivedfrom the host system 44 during a time interval t₁ '-t₁ " within theperiod t₁ -t₂, as indicated at (B) in FIG. 4. Then, as the RMMV 82, FIG.2, of the power switching circuit 42 goes high in response to theexternal stepping pulses, the power switch 80 will be closed to permitthe stepper motor windings 70 to be energized from the high power supply74, as at (D) in FIG. 4. The external stepping pulses will also bedirected through the signal selector circuit 62 into the stepper motorcontrol circuit 40, with the result that the stepper motor 32 rotates tocause the transducer 30 to travel from track Tn to track Tn+3 on thedisk 12.

As desired, the illustrated circuitry of the disk drive 10 may bemodified to maintain the stepper motor 32 out of rotation in the face ofsuch possible external stepping pulses incoming when the "motor on"signal is high. Even if the stepper motor 32 is so left out of rotationin order to save power, the new destination track represented by theseexternal pulses will be stored on the first track counter 56. Therefore,when the "motor on" signal subsequently goes low, the transducer 30 willbe positioned on that new destination track.

We have nevertheless employed the illustrated circuitry because thestepping pulses supplied from the host system when the "motor on" signalis high are mostly for recalibration, that is, for returning thetransducer to Track Zero on the disk. The repositioning of thetransducer on the latest destination track after the period t₁ -t₂according to our invention also requires that the transducer be returnedto Track Zero preparatory to being repositioned on the latestdestination track. Accordingly, if the transducer has already beenpositioned on Track Zero before the "motor on" signal goes low at thetime t₂, the repositioning of the transducer will be unnecessary. It isof course possible that after having been positioned on Track Zero, thetransducer be slightly displaced therefrom during the period t₁ "-t₂.Even in that case, however, the transducer will be repositioned on TrackZero in a much shorter time than when the stepper motor 32 is helddeenergized in spite of the external stepping pulses supplied when the"motor on" signal is high.

Thus the latest destination track before the time t₂ may be either trackTn or track Tn+3 depending upon whether the stepper motor 32 was drivenin response to the external stepping pulses supplied during the periodt₁ -t₂. Either way, since the stepper motor 32 is held completelydeenergized during the period t₁ -t₂ or the periods t₁ -t₁ ' and t₁"-t₂, the transducer 30 may be displaced from the latest destinationtrack Tn or Tn+3 because of mechanical vibrations or shocks that may beexerted on the disk drive 10 during such period or periods. Ourinvention makes it possible to automatically reposition the transduceron the latest destination track Tn or Tn+3 when, or after, the "motoron" signal goes low at the time t₂ commanding the disk drive motor 16 tobe set into rotation again.

We recommend that the repositioning of the transducer be not startedimmediately when the "motor on" signal goes low at the time t₂. Asindicated at (C) in FIG. 4, a large starting current will usually flowthrough the disk drive motor 16 when the "motor on" signal goes low atthe time t₂. Should the repositioning operation be started at this timet₂, a similarly large starting current would flow into the stepper motor32, too, because then the stepper motor would be connected to the highpower supply 74 via the power switch 80. The simultaneous flow of suchlarge starting currents to the two motors 16 and 32 is of courseobjectionable.

We therefore suggest that the repositioning of the transducer 30 bestarted at a time t₃ when the starting current of the disk drive motor16 subsides to a predetermined level slightly above the normal magnitudeof the motor current. It is toward this end that the repositioning startsignal input e, FIG. 1, of the repositioning circuit 88 is connected tothe unshown motor current detector circuit built into the disk drivemotor control and drive circuit 20.

However, as will be understood from FIG. 2, the low power switch 78 ofthe power switching circuit 42 will become closed at the time t₂ whenthe "motor on" signal goes low. The five volt supply voltage will thenbe impressed to the stepper motor 32, although this low supply voltageserves no useful purpose at this time.

Then, at the time t₃, the repositioning circuit 88 will start generatingthe signals for repositioning the transducer 30 on the latestdestination track on the disk 12, in response to the repositioning startsignal from the disk drive motor control and drive circuit 20. Thetransducer 30 must first be positioned on Track Zero before beingrepositioned on the latest destination track.

Accordingly, as indicated at (E) and (F) in FIG. 4, the generators 96and 98, FIG. 3, of the repositioning circuit 88 will generate theinternal stepping pulses and internal stepping direction signalnecessary for temporarily positioning the transducer on Track Zero.Applied to the RMMV 82, FIG. 2, of the power switching circuit 42, theinternal stepping pulses will cause the high power switch 80 to beclosed for application of the twelve volt supply voltage to the steppermotor 32. The low power switch 78, which has been closed, will open uponapplication of the internal stepping pulses to the RMMV 82.

As will be seen from (G) in FIG. 4, the repositioning state signal fromits generator 100, also included in the repositioning circuit 88, willgo low in response to the repositioning start signal to indicate thestart and progress of transducer repositioning. A reference back to FIG.1 will reveal that the repositioning state signal is applied directly tothe AND gates 102 and 106 of the stepping signal selector circuit 62.Thus disabled, the AND gates 102 and 106 will inhibit the application ofthe external stepping pulses and stepping direction signal from the hostsystem 44 to the stepper motor control circuit 40. The repositioningstate signal is also applied directly to the NAND gates 118 and 130thereby preventing the delivery of the "ready" signal and read data tothe host system 44.

The repositioning state signal is, however, inverted before beingapplied to the AND gates 104 and 108 of the stepping signal selectorcircuit 62. These AND gates 104 and 108 are therefore enabled to permitthe passage therethrough of the internal stepping pulses and steppingdirection from the repositioning circuit 88. Thus the stepper motorcontrol circuit 40 will respond to the internal stepping pulses andstepping direction signal by applying the corresponding control signalsto the stepper motor drive circuit 38, which in turn will cause thestepper motor windings to be energized from the high power supply 74accordingly.

It will be observed from (F) in FIG. 4 that the internal steppingdirection signal remains low after the time t₃, commanding the travel ofthe transducer 30 radially outwardly of the disk 12. Thus the transducer30 will start traveling radially outwardly of the disk 12 at the time t₃until the transducer arrives at the outermost Track Zero on the disk ata time t₄.

Upon arrival of the transducer 30 at Track Zero, the "track zero"detector circuit 94 will ascertain the fact on the bases of both theoutput from the optical "track zero" sensor 36 and the first phasecontrol signal delivered from stepper motor control circuit 40 tostepper motor drive circuit 38. The output from the "track zero"detector circuit 94 will be impressed to the input i of therepositioning circuit 88 and, therefore, to the internal steppingdirection signal generator 98, FIG. 3, included in the repositioningcircuit. Thereupon the internal stepping direction signal will go high,commanding the travel of the transducer 30 radially inwardly of the disk12. The internal stepping pulse generator 96 will continue theproduction of internal stepping pulses.

FIG. 1 shows that the output from the "track zero" detector circuit 94is also impressed to the reset input of the second track counter 90.Therefore, reset at the time t₄, the second bidirectional track counter90 will start counting the internal stepping pulses from the output a ofthe repositioning circuit 88 in an increasing direction, since then theinternal stepping direction signal from the output b of therepositioning circuit is high. The resulting output B from the secondtrack counter 90 represents the current track position of the transducer30, as contrasted with the output A from the first track counter 56which represents the latest destination track commanded by the externalhost system 44 before the time t₂. The latest destination track in thiscase is track Tn+3 if we assume that the stepper motor 32 was driven inresponse to the external stepping pulses during the period t₁ -t₂.

The comparator 92 will constantly compare the outputs A and B from thetwo track counters 56 and 90 during the radially inward travel of thetransducer 30 toward the latest destination track Tn+3. Initially, ofcourse, A will be greater than B, so that the comparator 92 will producefrom its (A>B) output a signal commanding the internal steppingdirection signal generator 98 to remain high in order to cause thecontinuation of the radially inward travel of the transducer 30.

Possibly, the transducer 30 may overrun the latest destination trackTn+3 for some reason or other. In that case, since A becomes less thanB, the comparator 92 will produce from its (A<B) output a signalcommanding the internal stepping direction signal generator 98 to go lowin order to cause the reversal of the traveling direction of thetransducer 30.

FIG. 4 shows that the transducer arrives at the latest destination trackTn+3 at a time t₅. Thereupon the comparator 92 will produce from its(A=B) output a signal commanding the internal stepping pulse generator96 to discontinue the production of the internal stepping pulses, thestepping direction signal generator 98 to go low, and the repositioningstate signal generator 100 to go high.

Then, as the output c of the repositioning circuit 88 goes high, the ANDgates 102 and 106 of the stepping signal selector circuit 62 will beenabled to permit the passage of the external stepping pulses andstepping direction signal from the host system 44 on to the steppermotor control circuit 44. The NAND gates 51 and 56 will also be enabledto permit the delivery of the "ready" signal and read data to the hostsystem 44.

Since the "motor on" signal has been low since the time t₂, as at (A) inFIG. 4, the host system 44 may put out a new seek command during theperiod t₃ -t₅ when the disk drive 10 is in the act of repositioning thetransducer 30 on the previous destination track Tn+3. The newdestination track will then immediately replace the previous destinationtrack in the first track counter 56, and the comparator 92 will comparethe current track position of the transducer 30 with the new destinationtrack, so that the transducer will be repositioned on the newdestination track. If the new destination track is radially outward ofthe current transducer position, that is, if A becomes less than B, thenthe comparator 92 will cause the internal stepping direction signal togo low. The transducer 30 will be subsequently repositioned on the newdestination track through the procedure set forth above.

Upon completion of transducer repositioning at the time t₅, the lowpower switch 78, FIG. 2, of the power switching circuit 42 will beclosed since the inverted "motor on" signal is then high and since nostepping pulses are being applied to the RMMV 82. Therefore, asindicated at (D) in FIG. 4, the five volt supply voltage will beimpressed to the stepper motor 32 in order to hold the transducer 30repositioned on the latest destination track.

At (B) in FIG. 4 is shown a series of external stepping pulses deliveredfrom the host system 44 during a subsequent period t₆ -t₇ for having thetransducer 30 positioned on some track Tx other than the latestdestination track. Then, as indicated at (D) in FIG. 4, the powerswitching circuit 42 will switch the stepper motor 32 from the five voltpower supply 72 to the twelve volt power supply 74 in response to theexternal stepping pulses. Energized from the high power supply 74, thestepper motor 32 will operate to cause the transducer 30 positioned onthe new destination track Tx.

SECOND FORM

In an alternate disk drive 10a shown in FIG. 5 we have employed abipolar drive stepper motor 32a in substitution for the four phase drivestepper motor 32 of the FIG. 1 disk drive 10. Per se well known in theart, the bipolar drive stepper motor 32a has two groups of fixedwindings 150 and 152, with each group comprised of two or more suchwindings. The fixed windings 150 and 152 are disposed at constantangular spacings about the axis of rotation of a rotor 154.

A bipolar drive circuit 38a for the stepper motor 32a comprises a bridgeconnection of four switching transistors 156, 158, 160 and 162 connectedbetween one group of stepper motor windings 150 and a direct currentpower supply 164. Another bridge connection of four switchingtransistors 166, 168, 170 and 172 is connected between the other groupof stepper motor windings 152 and the power supply 164. It will be notedthat the transistors 156, 160, 166 and 170 are pnp transistors whereasthe transistors 158, 162, 168 and 172 are npn transistors. Consequently,the first group of windings 150 are energized forwardly when thetransistors 156 and 162 are both conductive, and reversely when thetransistors 158 and 160 are both conductive. The second group ofwindings 152 are energized forwardly when the transistors 166 and 172are both conductive, and reversely when the transistors 168 and 170 areboth conductive.

The construction and operation of the stepper motor 32a and its bipolardrive circuit 38a as so far described are conventional, and therein liesno feature of our invention. The novel features of our invention willappear in the course of the following description.

Like the stepper motor control circuit 40 of the FIG. 1 disk drive 10, acontrol circuit 40a for the bipolar drive circuit 38a has two inputsconnected respectively to the two output lines 64 and 66 of the steppingsignal selector circuit seen at 62 in FIG. 1. The stepper motor controlcircuit 40a has four output lines 174, 176, 178 and 180 connected via apower switching circuit 42a to the bases of the transistors 156-162 and166-172 of the bipolar drive circuit 38a. Thus the stepper motor controlcircuit 40a puts out stepper motor control signals over the lines174-180 in response to either the external stepping pulses and steppingdirection signal from the host system 44 or the internal stepping pulsesand stepping direction signal from the repositioning circuit 88.

The power switching circuit 42a of this disk drive 10a differs from thecorresponding circuit 42 of the FIG. 1 disk drive 10 in being connectedbetween stepper motor control circuit 40a and drive circuit 38a. Thepower switching circuit 42a comprises four NAND gates 182, 184, 186 and188 and four AND gates 190, 192, 194 and 196.

The first output line 174 of the stepper motor control circuit 40a isconnected on one hand to the first NAND gate 182 and thence to the baseof the first transistor 156 of the bipolar drive circuit 38a and, on theother hand, to the first AND gate 190 and thence to the base of thefourth transistor 162 of the bipolar drive circuit. The second outputline 176 of the stepper motor control circuit 40a is connected on onehand to the second NAND gate 184 and thence to the base of the thirdtransistor 160 of the bipolar drive circuit 38a and, on the other hand,to the second AND gate 192 and thence to the base of the secondtransistor 158 of the bipolar drive circuit. The third output line 178of the stepper motor control circuit 40a is connected on one hand to thethird NAND gate 186 and thence to the base of the fifth transistor 166of the bipolar drive circuit 38a and, on the other hand, to the thirdAND gate 194 and thence to the base of the eighth transistor 172 of thebipolar drive circuit. The fourth output line 180 of the stepper motorcontrol circuit 40a is connected on one hand to the fourth NAND gate 188and thence to the base of the seventh transistor 170 of the bipolardrive circuit 38a and, on the other hand, to the fourth AND gate 196 andthence to the base of the sixth transistor 168 of the bipolar drivecircuit.

All the NAND gates 182-188 and AND gates 190-196 of the power switchingcircuit 42a have additional inputs connected to the "motor on" signalline 46 via the NOT circuit 68. Accordingly, when the "motor on" signalis low so that the output from the NOT circuit 68 is high, the NANDgates and AND gates of the power switching circuit 42a are all enabledto permit the passage of the stepper motor control signals from thecontrol circuit 40a on to the bipolar drive circuit 38a. The outputlines 174 and 178 of the stepper motor control circuit 40a go high tocause the stepper motor windings 150 and 152 to be energized forwardly.The output lines 176 and 180 go high to cause the stepper motor windings150 and 152 to be energized reversely.

We have illustrated in FIG. 5 only the stepper motor 32a, stepper motordrive circuit 38a and control circuit 40a, and power switching circuit42a of the alternative disk drive 10a. The other details of constructionof this disk drive 10a can be exactly as set forth above in connectionwith the first disclosed disk drive 10 and with reference to FIGS. 1 and3.

OPERATION OF SECOND FORM

Reference may be had to the timing chart of FIG. 6 for the followingoperational description of the disk drive 10a. The "motor on" signal onthe host system output line 46 is shown at (A) in FIG. 6 to be low fromtime t₁ to time t₂. Since the "motor on" signal is inverted by the NOTcircuit 68, all the AND gate 190-196 of the power switching circuit 42ago low whereas all the NAND gates 182-188 go high. All the transistors156-162 and 166-172 of the stepper motor drive circuit 38a are thereforenonconductive during the period t₁ -t₂.

As has been mentioned with reference to FIG. 4 depicting the operationof the FIG. 1 disk drive 10, the host system 44 may put out steppingpulses during the high state of the "motor on" signal, as indicated at(B) in FIG. 6. Although the power switching circuit 42, FIG. 2, of thedisk drive 10 responded to such stepping pulses by connecting the highpower supply 74 to the stepper motor 32, the power switching circuit 42aof the alternate disk drive 10a has no means for responding to steppingpulses. Therefore, in this alternate disk drive 10a, the stepper motor32a remains unenergized in the face of the external stepping pulsessupplied during the high state of the "motor on" signal, as will benoted from (D) in FIG. 6. Of course, a modification may be made in thedisk drive 10a for energizing the stepper motor 32a in response to suchstepping pulses.

It is understood that the disk drive 10a includes the track counter 56,FIG. 1, for memorizing the latest destination track commanded by thehost system before the time t₁. After the "motor on" signal goes low atthe time t₂, the data transducer is to be automatically repositioned onthis latest destination track through the following procedure, since thetransducer may have been displaced therefrom during the period t₁ -t₂when the stepper motor 32a has been held unenergized.

When the "motor on" signal goes low at the time t₂ to command therotation of the disk drive motor, the NAND gates 182-188 and AND gates190-196 of the power switching circuit 42a are all enabled, so that thestepper motor control circuit 40a becomes possible to control thestepper motor 32a in response to the internal stepping pulses andstepping direction signal from the repositioning circuit 88.

At (B) in FIG. 6 is shown that in this alternate embodiment, therepositioning circuit 88 starts the production of internal steppingpulses immediately when the "motor on" signal goes low at the time t₂.It will also be noted from (C) in FIG. 6 that the internal steppingdirection signal remains low after the time t₂ to cause the transducerto be first positioned on Track Zero on the disk and then goes high at atime t₃ to cause the transducer to travel toward the latest destinationtrack. Then the transducer will be repositioned on the latestdestination track at a time t₄.

POSSIBLE MODIFICATIONS

Although we have shown and described our invention in very specificaspects thereof and as embodied in five and a quarter inch magnetic diskdrives, we recognize, of course, that our invention could be embodied inother forms and is not to be limited by the exact details of theforegoing disclosure. The following, then, is a brief list of possiblemodifications, alterations or adaptations of the illustrated embodimentswhich we believe all fall within the scope of our invention:

1. In the FIG. 1 disk drive 10 the repositioning of the transducer onthe latest destination track could be started immediately when the"motor on" signal went low at the time t₂ in FIG. 4, provided that thesystem power supply was of sufficiently large capacity.

2. In FIG. 4 the repositioning of the transducer on the latestdestination track could be started at the time t₃ upon lapse of apredetermined period after the "motor on" signal had gone low at thetime t₂, instead of by relying on the magnitude of the current being fedto the disk drive motor.

3. The FIG. 5 disk drive 10a could be modified to include another powersupply of smaller voltage for holding the stepper motor energized in theabsence of external or internal stepping pulses while the "motor on"signal was low, as in the FIG. 1 disk drive 10.

What we claim is:
 1. A power saving method for a data storage apparatushaving a data transducer for data transfer with a disklike record mediumhaving a multiplicity of annular data storage tracks arrangedconcentrically on at least one side thereof, the apparatus furtherhaving a disk drive motor for setting the record medium into rotationwhen a binary "motor on" signal is in a first state, and out of rotationwhen the "motor on" signal is in a second state, a seek motor forcausing the transducer to travel from track to track on the recordmedium, and a high and a low power supply for energizing the seek motor,the high power supply having a higher supply voltage than the low powersupply, which method comprises:(a) supplying seek data representative ofsuccessive destination tracks on the record medium on which thetransducer is to be positioned by the seek motor; (b) energizing theseek motor from the high power supply when the seek data is beingsupplied, in order to enable the seek motor to position the transduceron the successive destination tracks; (c) energizing the seek motor fromthe low power supply when the "motor on" signal is in the first statebut when no seek data is being supplied, in order to enable the seekmotor to hold the transducer on each destination track; (d) alwaysmemorizing the latest of the successive destination tracks representedby the seek data; (e) saving power by disconnecting the seek motor fromboth high and low power supplies when the "motor on" signal gains thesecond state and by holding the seek motor deenergized until the "motoron" signal subsequently regains the first state, with the consequentpossibility that while the seek motor is held deenergized, thetransducer may be displaced from the destination track on the recordmedium which has been represented by the seek data before the seek motorbecomes deenergized; and (f) repositioning the transducer on thememorized latest destination track on the record medium after the "motoron" signal regains the first state.
 2. The power saving method of claim1 wherein the data storage tracks on the record medium include areference track and wherein the transducer is repositioned on thememorized latest destination track on the record medium after beingtemporarily moved to the reference track.
 3. A data storage apparatusfor use with a disklike record medium having a multiplicity of annulardata storage tracks arranged concentrically on at least one sidethereof, the apparatus adapted to be coupled to a host system generatingexternal stepping pulses and an external stepping direction signal, theapparatus comprising:(a) a disk drive motor for imparting rotation tothe record medium; (b) a data transducer for data transfer with therecord medium while the record medium is in rotation; (c) a steppermotor for causing the data transducer to travel from track to track onthe record medium; (d) a stepper motor drive circuit having a high and alow power supply for selectively energizing the stepper motor, the highpower supply having a higher supply voltage than the low power supply;(e) first input means for inputting external stepping pulses and anexternal stepping direction signal from the host system, these pulsesand signal being conjointly representative of successive destinationtracks on the record medium on which the transducer is to be positionedby the stepper motor; (f) a stepper motor control circuit connectedbetween the first input means and the stepper motor drive circuit forcausing the stepper motor drive circuit to drive the stepper motor so asto cause the transducer to be positioned on the successive destinationtracks on the record medium represented by the external stepping pulsesand the external stepping direction signal; (g) second input means forinputting a binary "motor on" signal having a first state for causingthe disk drive motor to be set into rotation, and a second state forcausing the disk drive motor to be set out of rotation; (h) a powerswitching circuit connected between the second input means and thestepper motor drive circuit for causing the stepper motor to beenergized from the high power supply when the stepping pulses are beinginput, in order to enable the stepper motor to position the transduceron the successive destination tracks, for causing the stepper motor tobe energized from the low power supply when the "motor on"signal is inthe first state but when no stepping pulses are being input, in order toenable the stepper motor to hold the transducer on each destinationtrack, and for disconnecting the stepper motor from both high and lowpower supplies when the "motor on" signal gains the second state and byholding the stepper motor deenergized until the "motor on" signalsubsequently regains the first state, with the consequent possibilitythat while the stepper motor is held deenergized, the transducer may bedisplaced from the destination track on the record medium which has beenrepresented by the external stepping pulses and the external steppingdirection signal before the stepper motor becomes deenergized; (i)memory means connected to the first input means for storing the latestof the destination tracks represented by the external stepping pulsesand the external stepping direction signal; (j) first means connected tothe stepper motor control circuit for delivering thereto internalstepping pulses and an internal stepping direction signal, which aresimilar respectively to the external stepping pulses and the externalstepping direction signal, after the "motor on" signal regains the firststate, the stepper motor control circuit responding to the internalstepping pulses and the internal stepping direction signal for causingthe transducer to travel toward the latest destination track on therecord medium from which the transducer may have been displaced whilethe stepper motor is held deenergized, said internal stepping pulses andstepping direction signal being "internal" in that they are generated bythe data storage apparatus, as opposed to the external stepping pulsesand stepping direction signal which are generated externally to theapparatus by the host system; and (k) second means connected to thememory means and the first means for causing said first means todiscontinue the delivery of the internal stepping pulses to the steppermotor control circuit when the transducer is repositioned on the latestdestination track on the record medium.
 4. The data storage apparatus ofclaim 3 wherein the power switching circuit comprises:(a) a first powerswitch connected between the stepper motor and the high power supply ofthe stepper motor drive circuit; (b) a second power switch connectedbetween the stepper motor and the low power supply of the stepper motordrive circuit; (c) a pulse generator connected to the first input meansfor generating, in response to each external stepping pulse, an outputpulse of predetermined duration for closing the first power switch; and(d) logic circuit means connected to both the pulse generator and thesecond input means for closing the second power switch when the "motoron" signal is in the first state but when no external stepping pulsesare being input to the pulse generator.